Preparation of halogen substituted phosphoric acid esters



Jnited States Patent 3 121,106 PREPARATION OF lIALOGEN SUBSTITUTED PHOSPHORIC ACID ESTERS :orges Nagy, Montrouge, France, assignor to Manufacturers de Prodnits Chimiques de Nord Etabllssements Kuhlrnann, Paris, France, a corporation of France No Drawing. Filed Mar. 28, 1961, Ser. No. 98,750

Claims priority, application France Mar. 30., 1960 1 Claim. (Cl. 260-461) In French Patent No. 1,198,196 filed June 6, 1958, ere was described a method of preparing halogen-conining phosphoric acid esters, especially halogen-containg alkyl phosphates, which basically comprises reacting phosphoric acid oxy-halide with a primary alcohol rlogen-substituted in alpha and beta positions in the 'esence of a catalyst essentially comprising a metal of .e second group of the periodic table. The halogenlbstituted alkyl phosphates which are among the prerred phosphoric acid esters obtainable by that method in be represented by the following general formula P 0 (0 CHr-CiX-CHX-Rt) 3 PO(OR) 3 wherein R, R and R have the meanings previously ndicated for R and R The halogen-substituted phosphoric acid esters proluced as just described have valuable uses as fireproofing )1 ignifuge agents in thermoplastic and thermosetting resins, per se or compounded in various compositions such as paints, varnishes, coatings, laminates and the like.

The presence of this mixed ester in the triester product results in a number of drawbacks.

In the first place, the mixed ester undergoes by the action of heat an intramolecular and/ or inter-molecular alcoholysis with one or more molecules of mixed ester or triester, forming a phosphate which condenses and an alcohol which is released, in accordance with the reaction This alcoholysis results in an increase in the viscosity 3,121,106 Patented Feb. 11, 1964 "ice of the product and the liberation of the volatile alcohol is especially troublesome where the phosphate is used as a fire-proofing addition for plastics, causing exudation, decrease in the hardness of polyester laminates and similar objectionable effects.

Furthermore, after prolonged storage in the presence of humid air the oxyalkyl phosphoric acid ester undergoes a change, clouding over first at the surface then becoming turbid and opalescent throughout. The presence of the hydrophilic hydroxyl groups increases the watersolubility of the product and facilitates hydrolysis of the ester bond.

Lastly, in polyester laminates containing fire-proofing additions of the oxy-alkyl-neutralized, halogen-substituted phosphoric acid esters, it is found that the sheets tend to bleach or discolor, an effect that is not present when pure triester is used. Such d-iscoloring is, apparently, ascribable to the presence of the free alcohol groups in the mixed ester and to the incompartibility thereof with the conventional s'ming and the like compositions commonly used in connection with fibre glass mats and the like.

It is an object of this invention to improve on the aforementioned method of preparing halogen-substituted phos phoric acid esters so as to eliminate the shortcomings and problems heretofore encountered and achieve additional advantages to be specified below. I have discovered that this can quite simply be achieved if the hydroxyl group of the mixed ester is blocked by acylation. For that purpose, the improved method of preparing halogen-containing phosphoric acid esters by reacting a phosphoric acid oxyhalide with a primary alcohol containing alpha-beta halogen-substituted primary alcohol, in the presence of a catalyst comprising a metal of the second group of the periodic table and neutralizing with an epoxy compound, is characterized in accordance with the present invention, in that the hydroxyl groups formed in the reaction between the phosphoric acid ester and the epoxy compound are esterified with a suitable fatty acid derivative, preferably of the type having a short carbon chain.

As the esterifying derivative, ketenes and anhydrides of fatty acids may be used. The ketenes may be used in the free state or under the form of addition products with a suitable ketone. For instance, an acetyling agent can be ketene, isopropenyl acetate (acetone enol-acetate), and acetic anhydride and acid. Acetylation through gaseous ketene takes piace by bubbling the lcetene at about 50 G. into the phosphoric ester. Isopropenyl acetate reacts with the alcohol groups whereby acetone and acetic ester are formed as lay-products. Esterification is effected by simultaneous heating and distilling of the formed acetone. When acetic anhy-dride is used, complete acetylation is obtained when the mixture is heated one hour at C. The acetic acid formed is then removed by distillation in vacuo. The acidic phosphoric acid esters contained in the crude reaction mixture are then converted into a mixed ester having the general formula PO OR) 2 (OCHR CHR OOCR wherein R, R and R have the same meanings as above and R represents an alkyl group. The said halogen-containing phosphoric acid esters possess high heat stability and also a greatly improved resistance to moisture owing to the absence of any hydrophilic grouping in their molecule.

The method of the invention may be carried out in any suitable apparatus, such as a double-Walled autoclave provided with an anchor-type agitator, a riser column filled with Rasching rings, a thermoelectric temperature probe, a tube for the addition of the reagents, a dipper tube for the delivery of nitrogen and possibly the epoxy compound in gaseous form, and a safety pressure release device e.g. valve or burst disk. Temperature control is cs effected by circulation of a suitable intermediate fluid, e.g. of the diphenyl/dipheny-l oxide type.

The Raschig-ring filled column is provided at its top with a reflux head and a spiral condenser for recycling the vesicles of phosphoric acid oxychloride entrained with the hydrochloric acid stream during esterification. The condenser is connected with absorbed columns which are also filled with Raschig rings and arranged to operate in counterflow relation. The reflux head is connected through a downtlow cooler with receiver flasks serving to collect the lighter fractions during the vacuum distillation.

Two exemplary procedures for carrying out the method of the invention are now described for purposes of illustration but not of limitation.

Example 1 2.022 parts by weight of distilled 2,3-dibromopropanol- (1) and 459 parts phosphoric acid oxychlcride are mixed at ordinary temperature. 0.6 part magnesium turnings amalgam and to of the externporaneously prepared mixture are placed into the reactor. It will be understood that in case of an industrial-scale rather than a laboratory process, it would be convenient to introduce both reagents concurrently through separate metering pumps or feeders. The mixture is then heated gradually to 100-105 C. while bubbling nitrogen through it. The reaction is initiated at about 60 C. Into the reaction mass heated so as to remain at a temperature of about 100-105" C., the remaining reagents are then introduced so as to cause a large, but not a violent, rate of hydrochloric acid discharge. After all of the reagents were introduced, the mixture is heated fora further half hour at 105 C., and the negative pressure is gradually applied at the outlet from the absorbers. The temperature of the reaction mixture is then gradually raised to 130 C. and maintained at that point until no more hydrochloric acid is released. Then nitrogen gas is bubbled through to produce de-gasification at reduced pressure. The esterification is completed in about 4 to 5 hours. An aliquot part has then been taken to precise the acidity due to the acidic phosphoric esters. The itration is realized by alkalimetry in an ethanol-ethylacetate medium, the indicator used being bromothymol blue. The acidity is of about 0.20.3 gr. equivaL/kg, which corresponds to a content of approximately 1015% of phosphoric diester.

The reaction mixture is then cooled to 90100 C., under which the temperature calculated rate, or preferably a slight excess (from 22 to 33 parts) of ethyleneoxide is introduced. After one hour, the fixation is practically completed, which is confirmed through alkalimetric checking.

Then the stoichiometric quantity, or preferably a slight excess, of acetic anhydride (44 to 66 parts relatively to the acidity of the raw esterification product) is introduced and one heats for 1 hour to 100 C. After said time, the hydroxyl groups are wholly esterified, the formed acetic acid is removed, with a possible excess of acetic anhydrid, under vacuo of mm. Hg.

The volatile by-products formed during esterification (and chiefly comprising chlorodibromopropane) and the excess dibromopropanol are distilled away by gradually heating the liquid to 150 C. at a pressure of 1 mm. Hg. In this way 1,854 parts of tris (2,3-dibromopropyl) phosphate of technical grade were obtained, which was found to have the following analysis and characteristics:

The resulting halogen-substituted phosphor ester is found to possess excellent fireproofing characteristics.

Example 2 The esterification has been completed according to E1 ample 1; then, after neutralizing of the raw ester b means of ethylene oxide (as epoxy compound), gaseor ketene has been bubbled through the phosphoric acid 2 about 50 C.; a stoichiometric quantity (or a slight e) cess) of ketene (18 to 27 g. in function to the acidity c the raw esterifying product) has been introduced. Th excess of epoxy compound and =ketene has thereafter bee removed, if necessary, by degasification at reduced pres sure.

The volatile by-products formed during esterificatio: have been distilled off as explained in Example 1. Ther has been obtained 1,840 parts of technical tris(2,3-di bromopropyl) phosphate, having the same physical char acteristics as in Example 1.

It should be noted that the method of the inventioi can conveniently be carried out in a single apparatus i] which all of the various operating steps involved ca] readily be performed, including a neutralization of th crude ester by oxyalkylation and the subsequent esterifi cation of the free alcohol groups in the mixed ester Wili a suitable fatty acid derivative.

Important advantages of the method of this inventioi over the conventional techniques include:

1) In the conventional method the crude halogen substituted phosphoric acid ester, which is both too densr and too viscous to be subjected without further treatmen to the necessary acidic and alkaline washing steps, mus first be diluted with an appropriate solvent. After tht washing steps, the solvent must be removed and recov ered. With the present method on the other hand Il'lt procedure is greatly simplified since the use of a solven and of the washing steps is unnecessary, as well as the troublesome sedimentation and distillation operations for recovering the solvent.

(2) In the conventional method the alkaline washing step has resulted in a loss of the phosphoric acid ester: since these are carried into the washing solution. Witl the process of the invention such acidic phosphates car be retained in the form of a neutral mixed ester in the final product, thereby resulting in an increase in yield by a factor of 10 to 15%. The presence of the mixed ester does not significantly affect the halogen content in the phosphate product and leaves the fireproofing properties of the product practically unchanged.

What I claim is:

A neutral halogen-substituted phosphoric acid ester of the formula:

alkyl, R is selected from the group consisting of hydrogen and lower alkyl, and X is a halogen atom.

References Cited in the file of this patent UNITED STATES PATENTS 2,791,574 Lanham May 7, 1957 2,830,069 Smith Apr. 8, 1958 2,909,559 Lanham Oct. 20, 1959 FOREIGN PATENTS 1,198,196 France June 8, 1959 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIQN atent 1110. 3,121,106 February 11,, 1964 Georges Nagy It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 42, for "itration read titration a,

Signed and sealed this 30th day of June 1964.

SEAL) ttes t:

NEST W. SWIDER EDWARD J. BRENNER .ttesting Officer Commissioner of Patents 

